/************************************************************************************************
 * libs/libc/misc/lib_crc16xmodem.c
 *
 * SPDX-License-Identifier: Apache-2.0
 *
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.  The
 * ASF licenses this file to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance with the
 * License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
 * License for the specific language governing permissions and limitations
 * under the License.
 *
 ************************************************************************************************/

/* "Programmers may incorporate any or all code into their programs,
 *  giving proper credit within the source. Publication of the
 *  source routines is permitted so long as proper credit is given
 *  to Stephen Satchell, Satchell Evaluations and Chuck Forsberg,
 *  Omen Technology."
 */

/* References:
 *
 *   crc16xmodem_tab calculated by Mark G. Mendel, Network Systems Corporation.
 *   crc16part() logic derived from article Copyright (C) 1986 Stephen
 *    Satchell.
 */

/************************************************************************************************
 * Included Files
 ************************************************************************************************/

#include <sys/types.h>
#include <stdint.h>

#include <nuttx/crc16.h>

/************************************************************************************************
 * Private Data
 ************************************************************************************************/

/* crc16xmodem_tab calculated by Mark G. Mendel, Network Systems Corporation
 * The poly is 0x1021 (x^16 + x^12 + x^5 + 1)
 */

static const uint16_t crc16xmodem_tab[256] =
{
  0x0000,  0x1021,  0x2042,  0x3063,  0x4084,  0x50a5,  0x60c6,  0x70e7,
  0x8108,  0x9129,  0xa14a,  0xb16b,  0xc18c,  0xd1ad,  0xe1ce,  0xf1ef,
  0x1231,  0x0210,  0x3273,  0x2252,  0x52b5,  0x4294,  0x72f7,  0x62d6,
  0x9339,  0x8318,  0xb37b,  0xa35a,  0xd3bd,  0xc39c,  0xf3ff,  0xe3de,
  0x2462,  0x3443,  0x0420,  0x1401,  0x64e6,  0x74c7,  0x44a4,  0x5485,
  0xa56a,  0xb54b,  0x8528,  0x9509,  0xe5ee,  0xf5cf,  0xc5ac,  0xd58d,
  0x3653,  0x2672,  0x1611,  0x0630,  0x76d7,  0x66f6,  0x5695,  0x46b4,
  0xb75b,  0xa77a,  0x9719,  0x8738,  0xf7df,  0xe7fe,  0xd79d,  0xc7bc,
  0x48c4,  0x58e5,  0x6886,  0x78a7,  0x0840,  0x1861,  0x2802,  0x3823,
  0xc9cc,  0xd9ed,  0xe98e,  0xf9af,  0x8948,  0x9969,  0xa90a,  0xb92b,
  0x5af5,  0x4ad4,  0x7ab7,  0x6a96,  0x1a71,  0x0a50,  0x3a33,  0x2a12,
  0xdbfd,  0xcbdc,  0xfbbf,  0xeb9e,  0x9b79,  0x8b58,  0xbb3b,  0xab1a,
  0x6ca6,  0x7c87,  0x4ce4,  0x5cc5,  0x2c22,  0x3c03,  0x0c60,  0x1c41,
  0xedae,  0xfd8f,  0xcdec,  0xddcd,  0xad2a,  0xbd0b,  0x8d68,  0x9d49,
  0x7e97,  0x6eb6,  0x5ed5,  0x4ef4,  0x3e13,  0x2e32,  0x1e51,  0x0e70,
  0xff9f,  0xefbe,  0xdfdd,  0xcffc,  0xbf1b,  0xaf3a,  0x9f59,  0x8f78,
  0x9188,  0x81a9,  0xb1ca,  0xa1eb,  0xd10c,  0xc12d,  0xf14e,  0xe16f,
  0x1080,  0x00a1,  0x30c2,  0x20e3,  0x5004,  0x4025,  0x7046,  0x6067,
  0x83b9,  0x9398,  0xa3fb,  0xb3da,  0xc33d,  0xd31c,  0xe37f,  0xf35e,
  0x02b1,  0x1290,  0x22f3,  0x32d2,  0x4235,  0x5214,  0x6277,  0x7256,
  0xb5ea,  0xa5cb,  0x95a8,  0x8589,  0xf56e,  0xe54f,  0xd52c,  0xc50d,
  0x34e2,  0x24c3,  0x14a0,  0x0481,  0x7466,  0x6447,  0x5424,  0x4405,
  0xa7db,  0xb7fa,  0x8799,  0x97b8,  0xe75f,  0xf77e,  0xc71d,  0xd73c,
  0x26d3,  0x36f2,  0x0691,  0x16b0,  0x6657,  0x7676,  0x4615,  0x5634,
  0xd94c,  0xc96d,  0xf90e,  0xe92f,  0x99c8,  0x89e9,  0xb98a,  0xa9ab,
  0x5844,  0x4865,  0x7806,  0x6827,  0x18c0,  0x08e1,  0x3882,  0x28a3,
  0xcb7d,  0xdb5c,  0xeb3f,  0xfb1e,  0x8bf9,  0x9bd8,  0xabbb,  0xbb9a,
  0x4a75,  0x5a54,  0x6a37,  0x7a16,  0x0af1,  0x1ad0,  0x2ab3,  0x3a92,
  0xfd2e,  0xed0f,  0xdd6c,  0xcd4d,  0xbdaa,  0xad8b,  0x9de8,  0x8dc9,
  0x7c26,  0x6c07,  0x5c64,  0x4c45,  0x3ca2,  0x2c83,  0x1ce0,  0x0cc1,
  0xef1f,  0xff3e,  0xcf5d,  0xdf7c,  0xaf9b,  0xbfba,  0x8fd9,  0x9ff8,
  0x6e17,  0x7e36,  0x4e55,  0x5e74,  0x2e93,  0x3eb2,  0x0ed1,  0x1ef0
};

/************************************************************************************************
 * Public Functions
 ************************************************************************************************/

/************************************************************************************************
 * Name: crc16xmodempart
 *
 * Description:
 *   Continue CRC calculation on a part of the buffer.
 *
 *   Return a 16-bit CRC-XMODEM of the contents of the 'src' buffer, length
 *   'len', using the polynomial 0x1021 (x^16 + x^12 + x^5 + 1).
 *
 *   The following checksums can, among others, be calculated by this
 *   function, depending on the value provided for the initial seed and
 *   the value the final calculated CRC is XORed with:
 *
 *   - Alias: CRC-16/ACORN, CRC-16/LTE, CRC-16/V-41-MSB, XMODEM, ZMODEM
 *     https://reveng.sourceforge.io/crc-catalogue/16.htm#crc.cat.crc-16-xmodem
 *     poly: 0x1021 initial seed: 0x0000, xor output: 0x0000
 *
 ************************************************************************************************/

uint16_t crc16xmodempart(FAR const uint8_t *src, size_t len, uint16_t crc16val)
{
  size_t i;

  for (i = 0; i < len; i++)
    {
      crc16val = crc16xmodem_tab[((crc16val >> 8) & 0xff) ^
                 src[i]] ^ (crc16val << 8);
    }

  return crc16val;
}

/************************************************************************************************
 * Name: crc16xmodem
 *
 * Description:
 *   Return a 16-bit CRC-XMODEM of the contents of the 'src' buffer, length
 *   'len', using the polynomial 0x1021 (x^16 + x^12 + x^5 + 1).
 *
 *   The following checksums can, among others, be calculated by this
 *   function, depending on the value provided for the initial seed and
 *   the value the final calculated CRC is XORed with:
 *
 *   - Alias: CRC-16/ACORN, CRC-16/LTE, CRC-16/V-41-MSB, XMODEM, ZMODEM
 *     https://reveng.sourceforge.io/crc-catalogue/16.htm#crc.cat.crc-16-xmodem
 *     poly: 0x1021 initial seed: 0x0000, xor output: 0x0000
 *
 ************************************************************************************************/

uint16_t crc16xmodem(FAR const uint8_t *src, size_t len)
{
  return crc16xmodempart(src, len, 0);
}
